Protists I (draft1)

Protists I (draft1) - Protista I Primitive and ancient...

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Primitive and ancient members of the Domain Archaea and Eubacteria (both prokaryotes) were the first living organisms to inhabit this planet circa 3.5 billion years ago. Organisms in the Domain Eukaryota evolved some time later, with the fossils of primitive protists dating back to the late Proterozoic era. Most biologists are in agreement that protists arose from primitive bacteria by way of more than one ancestral group. Various phyla of protists, therefore, represent separate evolutionary lineages or are polyphyletic in origin. Some protists are plant-like and are primarily autotrophic (they produce their own food), some are fungus-like and are absorptive heterotrophs. Ohters are animal-like and are heterotrophs themselves however they ingest their food. In this exercise, you will observe and study four phyla of animal-like protists. Protista I To an animal biologist, the animal-like Protists (those without chlorophyll), were described as protozoans (formerly a phylum designation). We will use this term to describe all unicellular, animal like protists, but it is important to realize that the term protozoa is not a taxonomic designation. The protozoa are most certainly descendant from those forms of life that gave rise to eumetazoans (multicellular organisms). Protists present today, however, have had a long evolutionary history and may be considerably different from their more primitive ancestors. It is therefore unreasonable to describe the protozoa as “primitive” as is commonly done. We describe protozoa as unicellular (cytoplasmic organization) as all functions are preformed with the limits of a single plasma membrane. Even though there are no tissues or organs in protists, there is a division of labor within the organism not seen in more primitive bacteria. This division of labor within the organism are characterized by specific organelles. In addition, some protozoans may associate together to form colonies, and there may be division of labor among members of a colony. Amoeba protus Currently taxonomists have described over 65,000 different protozoan species with over half of these organisms exant. These extant Protozoa live in many different environments; they can drift in the ocean and are the main components of zooplankton , creep across vegetation in fresh water rivers and ponds, crawl in deep soil, and even reproduce in the bodies of other organisms.
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